Volvo A/C question

I don't know a lot about HVAC systems, so I need some help.

The air conditioning in my 1998 Volvo V70R works...but only for about five or ten minutes. It's been this way for the two years that I've owned the car, and hasn't really bothered me, but I really should get this working properly.

I don't think anything in the system has been replaced, and I don't think that I have any leaks.

I have a vacuum pump and a set of gauges.

I know that you check for leaks by drawing a vacuum on an empty system and then watching for changes on the gauges, but assuming you have a system that's not leaking, is there any way to get the proper amount of refrigerant in there without fully evacuating the system down and then starting from zero?

I'm not talking about just dumping in cans of 134 until it works. Can you accurately get to the proper volume if you're starting with a partially filled system?

If it works steadily for 5-10 minutes before giving up, your refrigerant is probably fine and shouldn't be messed with. Low refrigerant will cause the compressor to short cycle repeatedly with lukewarm air, not give up after working well for a short period.

These cars have a known issue where the AC compressor clutch wears down prematurely due to repeated cycling, and after enough wear, the clutch only engages for a few minutes before overheating and releasing.

The correct fix is to replace or re-shim the clutch. Some people do it with bread clips.

https://volvoforums.com/forum/volvo-850-16/c-compressor-clutch-reshimming-6665/

https://www.matthewsvolvosite.com/ac-shim-fix-are-zip-ties-the-new-bread-clips/

To directly answer your question, no, there isn't unless you have a recovery system. The way I did it on my V70 was just a full evac/vacuum before filling with the proper weight.

I don't think so.  The expensive machines will pull everything out, recycle it, pull a vacuum and hold it. After a while checking for leakage they pump the exact amount the car calls for.

All I've ever done is put gauges on the vehicle, check the ambient temp and add 134 until the gauges read what they should when revving the car to about 2000 rpm.  If I've had the system apart there are more steps with oil etc. I've tried the digital scale method trying to get it exact but it isn't like we are recharging a fridge that may take only 10-12oz.

Use the $100 they will hit you to hook it to the machine for something else. You'll be chasing about 2 degrees F

In reply to pointofdeparture :

I seem to recall hearing about that issue when I was shopping for the car, but couldn't find the details again when I started looking into this past week.

I'll check those links out. Thanks.

If it works properly for a few minutes, there is something other than charge level going on.  Control unit is reading an incorrect pressure or something and shutting it off, or the clutch is slipping, as suggested above.

Next time it quits, find a long stick and push on the face of the clutch.  While understanding all the safety rules, if you tap the clutch and it engages, boom.  Reshim. 

In reply to Streetwiseguy :

A few years ago, the a/c clutch on my 2005 Tacoma stopped working. There was a guy on eBay selling clutch kits, which were about $700 cheaper than replacing the Toyota compressor. 

 I also had a similar thing going on with the PTO clutch on my lawnmower last year. 
 

I wonder if I have a similar situation going on here. On the mower, the clutch had worn down to the point to where the electro magnet could no longer overcome the gap. Sounds reasonable?

It is common on the compressor used on whiteblock Volvos to develop a weak compressor clutch.  The usual symptom is that the A/C works, and then when the electromagnet in the clutch gets hot, it doesn't have enough power to stay engaged anymore.

You MAY be able to take out a shim from the clutch hub to reduce the clearance.  Most likely you'll need a new compressor clutch.

...which is probably only available with a compressor, sadly.

I've done a few, and my S40 (whiteblock four) had a weak clutch that would disengage on days over 90F after a half hour.

I forget if I diagnosed this by spraying water on it to cool it off, or smacking it with a hammer using a long extension as a drift.

In reply to Woody (Forum Supportum) :

That is the typical failure mode of the Volvo compressors, yes.

I replaced the drier and compressor in mine with a new Nissens, thinking the clutch was probably too far gone at 240k mi, and it was a total PITA but doable in a long day. Volvo has a severe case of bracketitis going on with the alt/PS/AC and it really sucks to take it all apart and put it back together. Somewhere near 25 ridiculously-placed bolts had to be removed to get it all apart.

Were I to do it again I would try the zip tie "shim" method and just run it as long as possible.

In reply to pointofdeparture :

That sounds like an appealing solution to me.

Plus one on shimming.  Just hope you never have HVAC stepper motor issues.  A whole 'nuther ball of E36M3.